Gas pressure regulated atomizer tip for gas/oil burner

ABSTRACT

A BURNER SUITABLE FOR FIRING A GASEOUS FUEL OR A COMBINATION OF A GASEOUS AND A LIQUID FUEL WITH THE GAS BEING USED TO ATOMIZE THE LIQUID FUEL. PRIMARY GAS IS INTRODUCED TANGENTIALLY INTO THE OIL STREAM IN THE THROAT OF A VENTURI NOZZLE DESIGNED TO EXPAND THE MIXTURE. SECONDARY GAS DISCHARGES THROUGH AN OUTER ANNULUS AND IMPINGES ON THE GAS-OIL MIXTURE DISCHARGING FROM THE VENTURI NOZZLE. THE SIZE OF THE ANNULUS FOR ADMITTING THE SECONDARY GAS IS RENDERED ADJUSTABLE BY AUTOMATICALLY MOVING THE OIL ATOMIZING NOZZLE IN AND OUT OF SAID ANNULUS, SO AS TO MAINTAIN CONSTANT GAS PRESSURE IN THE PRIMARY GAS TUBE AT ALL GAS INLET RATES. THE VELOCITY OF THE MIXTURE DISCHARGING FROM THE NOZZLE WILL THEN BE CONSTANT AT ALL GAS FLOW RATES. THE BURNER HAS GIVEN EXCELLENT RESULTS IN ATOMIZING FUEL OIL WITH GAS FLOWS AS LOW AS 17% OF THE TOTAL B.T.U. FIRED AT A HIGH FIRING RATE (30 G.P.H. OIL EQUIVALENT TOTAL FUEL IN THE CASE OF THE BURNER TESTED), AND ALSO WITH 50% GAS AT A LOW FIRING RATE (10 G.P.H. EQUIVALENT TOTAL FUEL).

Oct. 26, 1971 PEASE ETAL GAS PRESSURE REGULATED ATOMIZER TIP FOR GAS/OIL BURNER Filed June 16, 1970 Ric/70rd Ll Rel bo/J L m wv //A m m ww NN E a v e m P 1 MN I m 0 w \w m 5 k 5 Q Q mm 1 mm United States Patent Oifice Patented Oct. 26, 1971 US. Cl. 239407 3 Claims ABSTRACT OF THE DISCLOSURE A burner suitable for firing a gaseous fuel or a combination of a gaseous and a liquid fuel with the gas being used to atomize the liquid fuel. Primary gas is introduced tangentially into the oil stream in the throat of a venturi nozzle designed to expand the mixture. Secondary gas discharges through an outer annulus and impinges on the gas-oil mixture discharging from the venturi nozzle. The size of the annulus for admitting the secondary gas is rendered adjustable by automatically moving the oil atomizing nozzle in and out of said annulus, so as to maintain constant gas pressure in the primary gas tube at all gas inlet rates. The velocity of the mixture discharging from the nozzle will then be constant at all gas flow rates. The burner has given excellent results in atomizing fuel oil with gas flows as low as 17% of the total B.t.u. fired at a high firing rate (30 g.p.h. oil equivalent total fuel in the case of the burner tested), and also with 50% gas at a low firing rate (10 gph equivalent total fuel).

BACKGROUND OF THE INVENTION The field of art to which this invention pertains is that of a high-temperature combination gas/oil burner with good atomization of the liquid fuel by the gas over a broad range of firing rates and gas/oil ratios.

SUMMARY OF THE INVENTION When a liquid fuel such as No. 6 fuel oil is fired in a furnace, the oil, prior to combustion, must be atomized into fine droplets by some effective atomizing medium. In industrial furnaces, steam and air are widely used for atomization of liquid fuels. However, steam and compressed air are costly and make no significant thermal contribution to the flame. Furthermore, steam or air will tend to create undesired scale on heated ferrous metals, and also to have a decarburizing effect thereon. In contrast, gaseous fuel, e.g., natural gas, with its high calorific value, is an ideal medium for atomizing liquid fuel, provided that the gas pressure can be kept sufficiently high and constant for efficient atomization over a wide range of burner firing rates.

The present burner uses natural gas to atomize No. 6 fuel oil, but will give good performance with any gaseous fuel as an atomizing agent and virtually any atomized liquid fuel, including preheated tar or pitch. This combination gas/oil burner has proven capable of firing, on a B.t.u. basis, either 100% gas or up to 83% oil with a minimum of 17% gas required for atomization of the oil. The range of firing rates for the burner tested was to 30 g.p.h. oil (720 to 4300 s.c.f.h. natural gas); however, this burner design is adaptable to burners of any industrial capacity.

It is an object of the present invention to provide an improved liquid/ gaseous fuel burner which automatically maintains constant gas pressure required for good atomization of the liquid fuel.

Another object of the invention is to provide a burner which can fire gas over a wide range of rates above the minimum required for atomization of the liquid fuel.

Particular features of the present burner are:

1) Introduction of primary gas tangentially into the oil stream at the throat of the oil nozzle.

(2) Venturi nozzle for expanding the gas-oil mixture.

(3) Adjustable annulus for supplying secondary gas and maintaining constant the primary gas pressure.

(4) Guide means to keep the oil atomizing nozzle centered in the gas nozzle.

(5 Impingement of high velocity secondary gas stream on primary gas-oil mixture.

DESCRIPTION OF THE DRAWINGS In the annexed drawings:

FIG. 1 is a longitudinal vertical section of the subject burner;

FIG. 2 is a similar sectional view of said burner as installed in a refractory-lined casing within a large industrial furnace;

FIG. 3 is an enlarged sectional view of the forward end of the burner shown in FIG. 1;

FIG. 4 is a sectional view on the line 4-4 of FIG. 3.

DESCRIPTION OF THE INVENTION Referring to the drawings, the body of the burner 10 of this invention is preferably enclosed within a protective refractory-lined metal outer shell 11 which is provided with a large upper air inlet 12 and a plurality of smaller air outlet holes 13 in a forward air distributing member 14 for supplying combustion air to the burner 10. Said burner 10 projects forwardly through the port 15 in the refractories 16 of the furnace (not shown) to which it supplies heat.

Said burner 10 comprises a large tubular outer casing 17 which is provided with a substantially bell-shaped rear closure portion 18, a bottom inlet portion 19 for receiving gaseous fuel under suitably high pressure (typically about 40 p.s.i.), a communicating inner chamber compartment 20 and a gaseous fuel tube 21 having an inwardly flanged orifice 22 in the cap fitting 22' at its forward end.

Forwardly projecting in gas-tight relation through said rear closure portion 18, inner chamber 20 and gaseous fuel tube 21 is a reciprocably movable liquid fuel pipe 23, upon the forward end of which is threaded or otherwise attached a venturi type nozzle 24. The conical outer surface of the forward end of said nozzle 24 defines a tapering annular secondary or supplemental gaseous fuel outlet 25 with the gaseous fuel tube orifice 22. A plurality of spaced ports 26 extend inwardly and tangentially through the side walls 27 of the forward end of said nozzle 24 and are in communication with said gaseous fuel tube 21 to supply primary gaseous fuel. Said nozzle 24 is kept properly centered within the gaseous fuel tube 21 by means of a centering device such as a. spider or 'a radially perforated round plate 28.

The rear end of the liquid fuel pipe 23 is attached to a piston 29 and extends rearwardly within a corrugated flexible metal bellows portion 30 and a compression spring 31 bearing against a spring seat 32. A pressure adjusting screw 33 and spring release nut 34 are also provided. In operation, the spring loaded bellows 30 responds automatically to small changes in gas pressure in the chamber 20 and thereby enlarges or decreases the open area of the gas annulus 25 correspondingly, so as to maintain nearly constant the primary or atomizing gas pressure over the range of incoming gas flow rates, which tend to fluctuate with the furnace demand for heat. The spring expansion with decreases in gas pressure serves to close the annulus 2-5 to mantain constant the primary gas pressure, so that there is always a suflicient supply of gas for proper atomization of the oil.

In the specific embodiment of the invention as described, the venturi portion of the liquid fuel nozzle 24 is about A" in outer diameter and 1%" long, and its inner diam- 3 eter flares from A2" at its throat to A" at the mouth. Each of the tangential ports 26 in said nozzle 24 is .03 in diameter, and preferably consists of four equally spaced holes drilled at a forward inclination of 45 from horizontal. The outer face of the end portion of said nozzle 24 is tapered at an angle of 30 from horizontal. The gaseous fuel tube 21 has an interior diameter of 1%", and the diameter of its end orifice is with .002 clearance from the nozzle 24. The outside diameter of the liquid fuel pipe 23 (which is concentric within said pipe 21) may be Oil pressure is maintained at about 20 to 35 p.s.i.g., and the primary gas pressure is kept at approximately 40 p.s.i.g. as stated. Gas in excess of 720 s.c.f.h. serves as secondary gas.

We claim:

1. In combination with a liquid/gaseous fuel burner having a gaseous fuel tube with an orifice at its forward end, means to supply a gaseous fuel to said gaseous fuel tube, a reciprocably movable liquid fuel pipe extending within said gaseous fuel tube, and means to supply a liquid fuel to said liquid fuel tube, the improvement comprising: v

(a) a nozzle at the forward end of said liquid fuel pipe having (1) a longitudinally extending venturi orifice,

(2) a forward end defining an annular gaseous fuel outlet with said gaseous fuel tube orifice,

(3) a plurality of ports spaced from the forward end of said nozzle and extending inwardly from said gaseous'fuel tube and in communication tangentially with said venturi orifice, and

4 (b) means for varying the size of said annular gaseous fuel outlet so as to maintain the pressure in the gaseous fuel tube substantially constant despite variations in the incoming gaseous fuel flow rate.

2. A burner as defined in claim 1, wherein the means of subparagraph (b) includes means responsive to small variations in pressure in the gaseous fuel supply to the burner and connected to the liquid fuel pipe for varying the longitudinal position of said liquid fuel pipe within said gaseous fuel tube so as to vary the size of the annular gaseous fuel outlet.

3. A burner as defined in claim 2, wherein the pressureresponsive means comprises a spring-loaded bellows arrangement which functions to constrict or enlarge the annular gaseous fuel outlet.

References Cited UNITED STATES PATENTS 1,433,255 10/1922 Binks 239-417 X 1,793,154 2/1931 Bellem et a1. 239-410 1,826,163 10/1931 Barber et al. 239417 2,764,455 9/1956 Seibel 239-430 3,213,918 10/965 Rudzki et al 239-424 X LLOYD L. KING, Primary Examiner U.C. Cl. X.R. 

